Sutures are commonly used to hold together tissue that has been severed by injury, incision, or surgery to aid in the healing process or to apply pressure to blood vessels to stop bleeding. Sutures can be absorbable or non-absorbable. Non-absorbable sutures are made from inherently colorless materials such as silk, polypropylene, polyester, nylon, or ultra high molecular weight polyethylene (UHMWPE). Sutures are commonly in either braided multifilament or monofilament construction, but are sometimes also known in a twisted construction. The form of a suture is usually dictated by the stiffness or fiber modulus of its constituent fiber. Sutures require good pliability for their handling and knotting properties. Thus, fibers that are too stiff cannot be used in a monofilament form for larger suture sizes but rather in bundles of small denier filaments. These strands of multifilament are then braided together to form a suture. As the suture diameter gets larger, a core is usually added inside the braided sheath. Fibers with a modulus below about 600,000 psi can be used in monofilament form, although lower modulii are preferred. Thus, polyester and UHMWPE sutures are used in multifilament braids, while polypropylene is used as a monofilament suture. Some materials like nylon 66 with borderline properties are made in both multifilament and monofilament constructions. Natural fibers like silk that are fine denier can only be used in multifilament constructions.
Synthetic and most natural materials used to make sutures are without color. With the two basic constructions of braided multifilament and monofilament many types of sutures would be indistinguishable from other sutures even though their properties might be quite different. Thus, the value of coloring in sutures has long been recognized. Not only does color provide distinction between different types of sutures but is also known to aid the surgeon to keep track of sutures in the blood field during surgery.
Sutures are implantable devices and only specific colorants listed in the Code of Federal Regulations (CFR) for a particular suture material can be used. The regulations also put a limit on the maximum weight percent for each colorant for each suture material. Thus, there are limitations in colors available for all suture materials. There are also certain inherent limitations to how color can be added to some suture materials based on their polymer properties and how they are processed into sutures.
The advent of endoscopic surgery procedures has put additional pressure on surgeons to correctly identify sutures and their respective ends for proper tying of knots in confined spaces. During suturing it may be necessary for a physician to distinguish between the ends of similar sutures, which becomes more difficult when both ends of the sutures have an identical appearance of either no color or the same color.
One way to aid a surgeon in distinguishing an incoming end from an outgoing end of a suture, is to use a “half and half” suture, in which one half or one end is colored and the other half or end remains white. For example, Teleflex Medical of 1295 Main Street, Coventry, Conn. 06238, has made a polyester braided tape since 1998 in which one half of it has been dyed with D&C Green No. 6. So the tape has one end that is green and one end that is undyed white. However, a suture made from white UHMWPE yarn is not dyeable owing in part to the high crystallinity of the fiber and therefore cannot be dip dyed to distinguish one side from the other. To add color to a colorless braid of UHMWPE, it is therefore necessary to incorporate either a monofilament or a multifilament of a dyeable fiber material into the braided suture construction. This construction can then be immersed half way into a dye bath that will only color the dyeable fiber and not the UHMWPE fiber. Although it is highly unusual to co-braid a monofilament with multifilament yarn in a suture construction, monofilaments can be used for this application as they can bring a brighter color to the overall braid.
Although the half and half does allow the surgeon to distinguish between the incoming and outgoing ends of one individual suture strand, it offers no help when two or more of the same type of suture is being used. In these cases, there is no differentiation between the various incoming and outgoing ends of suture from each other.
Additionally, while the ends are distinguishable in an individual half and half suture, one half of the suture remains white and there can still be considerable white glare observed under bright lights, such as those used in endoscopic surgery. It is therefore also necessary to reduce the glare on the colorless portions of these sutures.
Accordingly, it is desirable to provide a UHMWPE suture which has distinguishable ends, a distinct junction, and has a reduced glare in the surgical field.